The present invention relates to a photographic printing apparatus, and more particularly relates to a printing apparatus which is adapted to use a paper magazine containing therein a rolled photographic paper. The invention also relates to a paper magazine for use with such an apparatus.
In photographic printing apparatus, it is usual to control correctively the exposures of the three primary color (blue, green and red) components of printing light based on the color densities of a negative picture frame in order to make a fine color print with proper color balance and density. For obtaining the proper exposures, there are several calculation equations well known in the art. According to one of the calculation equations, the proper exposure can be calculated numerically from the values of mean transmittance densities of a specific negative and a picture frame from which a color print is made. That is to say, the proper exposure is the sum of a standard exposure (constant) for the specific negative and an exposure which is the product of a coefficient and the difference in mean transmittance density between the two negatives. In practice, an exposure time for each color is calculated because that exposure is a value of the integration of illumination on a photographic paper with time, the luminosity of the printing light source being constant. The above-described constant and coefficient must be varied in accordance with several factors such as film balances, photographic paper balances, printing lens balances and so forth.
For this reason, conventional printing apparatus has a plurality of printing channels for establishing a constant and a coefficient so as to control correctively the exposure of each color in order to make a fine print with proper color balance and density. The printing channels are selectively used in accordance with combinations of paper balances, lens balances, film balances and so forth. The paper balance which represents the type of photographic paper depends on combinations of paper speeds or sensitivities, emulsion types and surface properties. The lens balance which represents the type of printing lens depends on combinations of printing magnifications, aperture F-numbers and the like. The film balance which represents the type of film such as negative films, reversal films, etc. depends on combinations of film speeds or sensitivities, film formats, and producers who supply films.
Such printing apparatus is adapted to use a paper supply magazine containing a rolled photographic paper therein and a paper take-up magazine in which an exposed photographic paper is wound. The photographic paper in the paper supply magazine is withdrawn therefrom frame by frame, and exposed to form thereon a latent image from a negative at an exposure station. Then the exposed photographic paper is taken up in the paper take-up magazine.
A problem with which conventional printing apparatus is attended is that a manual resetting of paper balance is necessary every time a different photographic paper contained in a paper magazine is used. This manual resetting is executed through keys or dials on an operation panel and is, therefore, troublesome in operation.